Commercial aircraft fly at very high altitudes. This is because, at least in part, the relatively thinner air at higher altitudes reduces drag. As a result, modern commercial aircraft fly in the range of approximately 30,000-45,000 feet above sea level (ASL), while private jets may fly as high as 51,000 feet ASL. And, while flying at this altitude increases efficiency, it also requires that some technical difficulties to be overcome.
One of these difficulties is that the air at these altitudes does not contain enough oxygen to sustain human life. At altitudes above approximately 12,000-14,000 feet ASL, most humans begin to suffer from altitude induced hypoxia. Early solutions to this problem included oxygen mask systems for providing additional oxygen directly to users. Such systems are still used in fighter aircraft, for example, where oxygen need only be provided for one or two users. In large commercial aircraft, however, oxygen mask systems are impractical due to, for example, the number of passengers, size and space requirements, and the need for passengers and flight attendants to be able to move about the cabin.
A more practical solution to this problem is to pressurize the cabin. This enables the cabin to simulate conditions at lower, safer altitudes (generally, similar conditions to those found at somewhere between 4,500 and 8,000 feet ASL). This feature was introduced in 1938 on the Boeing 307—the first commercial airliner with a pressurized cabin.
Conventionally, conditioned air is pumped into the cabin that is provided by, for example, bleed air off the compressor side of a turbine engine. Excess pressure in the cabin is then bled off using a Cabin Pressure Outflow Valve (CPOV). Conventional CPOVs do not, however, attempt to manage the airflow through and out of the valve. This can result in undesirable noise levels inside the cabin and additional drag on the fuselage of the aircraft, among other things.
It is with such considerations in mind that embodiments of valves for pressurized aircraft cabins are described.